It may not sound like much if the water was static in the root zone, but its not. Thats the drop in PH after the nute water just passes through that tote. The flow rate is roughly 15 oz / minute or about 7 gals/hr in that tote. Thats the volume that is passing through about 1 sq ft of fabric that is maybe 3/8" thick with roots in the bottom of the tote. So the PH is coming in a say 5.8 and coming out at 5.6 to 5.7 after it travels about 1 ft through the root zone. Looking at it that way, it seems pretty drastic to me.
I just did another rez change and this time I let the plain water circulate for a while at a PH of 6.8 before adding nutes or PHing down again. I also dropped the EC down to 900uS (450PPM on the .5 scale) this time. Thats the lowest Ive gone so far. I’ll monitor EC and PH and see how they do. Hopefully both will now be stable. That seems like an awefuly low EC, but Im near the end of flower, so maybe they dont need as much feed? We will see…
On the copper - it has been out for a week at least, but I wonder if maybe it did some damage to the roots? I cant think of any way to test that though.